The invention relates to a procedure for generating control data for an eye-surgery treatment apparatus that, by means of a laser device, separates tissue layers in the cornea of the eye, wherein, during operation of the laser device, a contact glass having a contact surface deforms the cornea into the shape of the contact surface, for which purpose the contact surface is first set, with a contact-surface vertex, onto a corneal vertex and, for the purpose of deforming the cornea, is then pressed against the latter, the procedure comprising the following steps: the control data for the laser device is generated in such a way that it specifies coordinates of target points for the laser device that are located in the cornea and, in the generation of the target-point coordinates, the deformation of the cornea, caused by the contact glass, that exists during operation of the laser device is considered.
The invention further relates to an eye-surgery treatment apparatus that comprises: a laser device for separating tissue layers of the cornea of the eye, a contact glass, which has a contact surface and which, during operation of the laser device, deforms the cornea into the shape of the contact surface, for which purpose the contact surface is first set, with a contact-surface vertex, onto a corneal vertex and, for the purpose of deforming the cornea, is then pressed against the latter, and a control device, which generates control data for the laser device in such a way that it specifies coordinates of target points for the laser device that are located in the cornea, and which, in the generation of the target-point coordinates, considers the deformation of the cornea, caused by the contact glass, that exists during the operation of the laser device.
The invention further relates to a procedure for eye-surgery treatment that, by means of a laser device, separates tissue layers in the cornea of the eye, wherein a contact glass having a contact surface is first set, with a contact-surface vertex, onto a corneal vertex and, for the purpose of deforming the cornea, is then pressed against the latter, such that the contact glass deforms the cornea into the shape of the contact surface, control data for the laser device being generated in such a way that it specifies coordinates of target points for the laser device that are located in the cornea and, in the generation of the target-point coordinates, the deformation of the cornea, caused by the contact glass, that exists during the operation of the laser device is considered.
Finally, in addition, the invention relates to a procedure for eye-surgery treatment that, by means of a laser device, separates tissue layers in the cornea of the eye, wherein, for the purpose of deformation, a contact glass having a contact surface is pressed against the cornea, such that the contact glass deforms the cornea into the shape of the contact surface, control data for the laser device being generated in such a way that it specifies coordinates of target points for the laser device that are located in the cornea and, in the generation of the target-point coordinates, the deformation of the cornea, caused by the contact glass, that exists during the operation of the laser device is considered.
For a long time, spectacles have constituted the classic way of correcting defective vision of the human eye. Now, however, increasing use is being made of refractive surgery, which corrects defective vision by altering the cornea of the eye. In such cases, the aim of all procedures of operation is purposefully to alter the cornea in order to influence the refraction of light. Differing procedures of operation are known for this purpose. Most widespread is that of so-called laser in-situ keratomileusis, also abbreviated as LASIK. In this case, a corneal lamella is first detached from the corneal surface on one side and folded to the side. This lamella can be detached by means of a mechanical microkeratome, or also by means of a so-called laser keratome, such as that distributed by, for example, Intralase Corp., Irvine, USA.
The latter produces a cut surface in the cornea through laser radiation. In this case, a plurality of processes, which are initiated by the laser radiation, take place in succession in the tissue. If the power density of the radiation is above a threshold value, an optical breakdown occurs, which produces a plasma bubble in the cornea. After the optical breakdown has occurred, the plasma bubble grows as a result of expanding gases. If the optical breakdown is not maintained, the gas produced in the plasma bubble is absorbed by the surrounding material and the bubble disappears again. Also possible are tissue-separating effects that act without a plasma bubble. For simplicity, all such processes are combined here under the term “optical breakdown”, i.e. this term is intended to include, not only the optical breakdown, but also the effects in the cornea that result therefrom.
For the purpose of producing the optical breakdown, the laser radiation is applied in a pulsed manner, the pulse length being less then 1 ps. As a result, for the respective pulse, the power density required to trigger an optical breakdown is achieved only in a confined spatial region. U.S. Pat. No. 5,984,916 shows clearly in this respect that the spatial area of the optical breakdown (in this case, of the interaction produced) is highly dependent on the pulse duration. A high degree of focusing of the laser beam, in combination with the aforementioned short pulses, therefore enables the optical breakdown to be applied very precisely in the cornea.
For the purpose of producing the thin lamella, a series of optical breakdowns is then produced at predefined points by means of the laser keratome, so as to realize a cut surface that detaches the lamella from the cornea underneath the latter.
After the lamella has been detached and folded to the side, in the case of the LASIK operation there is provision for use of an excimer laser, which removes the now exposed corneal tissue through ablation. After volume located in the cornea has been vaporized in this manner, the corneal lamella is folded back again to the original place. The LASIK procedure already in use, which, insofar as a laser keratome is used, is also designated as fs-LASIK, thus exposes a cap-shaped corneal lamella, folds back the latter and ablates the exposed tissue by means of an ablation laser.
It is also mentioned in the prior art that the correction of defective vision is produced in that a lens-shaped partial volume in the corneal tissue is isolated by means of the pulsed laser radiation. Such a depiction is found, for example, in WO 2005/011545 A1. However, devices are not yet correspondingly available on the market.
The precision with which the cut surface is produced is, of course, ultimately determinative for the optical correction. This applies quite particularly to advanced laser-surgery procedures of correction of defective vision, in which a volume located in the cornea is isolated through a three-dimensional cut surface and is thus rendered removable. Unlike in the case of the laser keratome, the position of the cut surface is then directly relevant to optical correction. In the case of the conventional LASIK method, by contrast, it is exclusively the precision with which the laser ablation is performed that is important for the quality of the optical correction, which is evident even from the fact that, in a great multiplicity of operations, the production of the corneal lamella is, or has been, effected by means of a mechanical blade whose operation is comparatively imprecise.
It is further known from WO 2005/011547 A1 that a contact glass, onto which the cornea of the eye is pressed, can be used in the case of laser-surgery apparatuses. This contact glass serves to impart a fixed, defined shape to the cornea and, at the same time, to fix the eye in place. The pressing onto the contact glass thus results in a deformation of the cornea, which is considered in the determination of the coordinates of the target points in that pressing-on and deformation is considered in a coordinate transformation, which, in the WO publication, is designated as a “contact pressure transformation” and which allows for a displacement of the target points. The printed publication gives transformation equations for the case of a combination of a spherical contact glass and a spherical corneal anterior surface. Although the publication mentions that further supplements are possible by means of correction terms, it does not describe such terms. The transformation equations mentioned therein therefore apply exclusively to spherical contact glasses and spherical corneal anterior surfaces, which, however, are not always the case.